SCIENCE & ENGINEERING NEWS

San Diego, CALIF. — Carl T. Hall reports that a single soccer-ball-shaped molecule of carbon sandwiched between gold electrodes has been fashioned into the smallest transistor ever built.

The tiny device, made by a team of physicists and chemists at the Lawrence Berkeley National Laboratory, is the latest wonder to emerge from the field known as nanotechnology, in which scientists are busy trying to fashion the working parts of a new generation of electronic devices.

The fruits of these labors are too small to be seen, measured on the scale of nanometers, or billionths of a meter. And for now, they amount to little more than laboratory curiosities.

But experts say it may someday be possible to incorporate single- molecule switches and tiny wires into unimaginably small supercomputers and “smart” devices.

“It’s going to happen, and it’s going to happen in our lifetimes,” said Mike Naughton, a physicist at Boston College who has been trying to coax arrays of elongated carbon wires, called nanotubes, to self-assemble in useful ways.

A report on the carbon-60 transistor project appeared this month in the British journal Nature. The research team was led by physicist Paul L. McEuen and chemist A. Paul Alivisatos, both of the Lawrence Berkeley lab and the University of California at Berkeley, and Hongkun Park, formerly of the Berkeley lab and now at Harvard University.

In a separate commentary appearing in the same science journal, physicist Leo Kouwenhoven of Delft University of Technology in the Netherlands said the researchers had succeeded in harnessing “the natural motion of molecules that are loosely bound to a gold surface.”

Exotic as that may sound, some practical applications already seem apparent to nanotechnology pioneers.

“The mechanical control of nanoscale objects will mean smaller, faster and more efficient versions of existing micro-electromechanic structures, an example of which is the accelerometer that triggers air bags in vehicles,” Kouwenhoven noted.

“Making something out of a single molecule like this is quite an achievement,” said Eric Wong, a physical chemist researching molecular electronics at the University of California at Los Angeles.

The new gizmo is the smallest example yet of the circuit-controlling workhorses known as “field-effect transistors.” It works like a subway turnstile for commuting electrons – electrons so well-controlled that just one particle at a time can be made to file through the gate, jumping from one gold surface to the other and then back again.

The Berkeley researchers first had to find a way to get the gold electrodes close enough together to capture single carbon molecules, rather than clumps of molecules that would gum up the subtle electrical and quantum forces that drive the single-molecule device.

“It’s a beautiful piece of work in that sense,” Naughton said. “They had to find a way to make the gaps small enough, and then they found a way to make the carbon molecules situate themselves in that gap. So once they did that, they had the makings of a transistor.”

The transistor works by applying a minute charge to the carbon-60, inducing a single electron on one electrode to hop off, bore through the “soccer ball” – an effect known as “quantum tunneling” – and then hop on the other electrode.

The single-electron current caused the carbon-60 to quiver as though suspended by tiny springs. In effect, the hopping electrons turned each little soccer ball into a “nanomechanical oscillator.”

It could point to a new strategy for memory storage in which a system of nano-scale switches and valves would hold the information. Many biological systems work along similar lines, such as the ion channels that control the flow of charged particles into and out of the cells of our bodies.

“There’s so much excitement here that you can see a lot of opportunity to make little systems where you apply a voltage and have something move,” McEuen said.

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